An extraction turbine is known that extracts steam from an intermediate stage of a steam turbine, and supplies the steam to a process system such as a plant for use (for example, Patent Literature 1). FIG. 7 illustrates configurations of a conventional steam turbine and peripherals thereof. In FIG. 7, a steam turbine 110 includes a high-pressure turbine 11, a low-pressure turbine 12, a governor valve 14 that controls a flow rate of steam to be supplied to the high-pressure turbine 11, and an extraction control valve 15 that controls a flow rate of steam to be supplied from the high-pressure turbine 11 to the low-pressure turbine 12. A generator 13 is directly connected to the steam turbine 110.
An electronic governor 51 is also provided as an operation control apparatus for a steam turbine, and the electronic governor 51 includes a speed controller 52 that generates a speed control output signal S11 based on an output target value of the steam turbine 110 and a speed signal S1 from a speed detector 41, an extraction pressure controller 53 that generates an extraction pressure control output signal S12 based on an extraction flow rate target value of the steam turbine 110 and an extraction pressure signal S2 from an extraction pressure detector 42, and an extraction map 54 for deriving opening degrees of the governor valve 14 and the extraction control valve 15 at an operation point determined depending on the speed control output signal S11 and the extraction pressure control output signal S12. The extraction map 54 is converted to generate a GV operation signal S21 for operating the governor valve 14 and an ECV operation signal S22 for operating the extraction control valve 15.